Method and apparatus for vibration detection

ABSTRACT

Apparatus for detecting vibration of an object adapted to rotate includes one or more vibration processors selected from: a direction-change processor adapted to detect changes in a direction of rotation of the object, a direction-agreement processor adapted to identify a direction of rotation of the object in at least two channels and identify an agreement or disagreement in direction of rotation identified by the at least two channels, a phase-overlap processor adapted to identify overlapping signal regions in signals associated with the rotation of the object, and a running mode processor adapted to identify an unresponsive output signal from at least one of the at least two channels. A method for detecting the vibration of the object includes generating at least one of a direction-change output signal with the direction-change processor, a direction-agreement output signal with the direction-agreement processor, a phase-overlap output signal with the phase-overlap processor, and a running-mode-vibration output signal with the running-mode processor, each indicative of the vibration the object.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-In-Part of and claims the benefitunder 35 U.S.C. §120 of U.S. patent application Ser. No. 10/820,957filed Apr. 8, 2004, which application is incorporated herein byreference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

This invention relates generally to vibration detection, and inparticular, to vibration detection methods and apparatus that canidentify a vibration in an object adapted to rotate in normal operation.

BACKGROUND OF THE INVENTION

Proximity detectors (also referred to herein as rotation detectors) fordetecting ferrous or magnetic objects are known. One application forsuch devices is in detecting the approach and retreat of each tooth of arotating ferrous object, such as a ferrous gear. The magnetic fieldassociated with the ferrous object is often detected by one or moremagnetic field-to-voltage transducers (also referred to herein asmagnetic field sensors), such as Hall elements or magnetoresistivedevices, which provide a signal proportional to a detected magneticfield (i.e., a magnetic field signal). The proximity detector processesthe magnetic field signal to generate an output signal that changesstate each time the magnetic field signal crosses a threshold.Therefore, when the proximity detector is used to detect the approachand retreat of each tooth of a rotating ferrous gear, the output signalis a square wave representative of rotation of the ferrous gear.

In one type of proximity detector, sometimes referred to as apeak-to-peak percentage detector (also referred to herein as a thresholddetector), the threshold signal is equal to a percentage of thepeak-to-peak magnetic field signal. One such peak-to-peak percentagedetector is described in U.S. Pat. No. 5,917,320 entitled DETECTION OFPASSING MAGNETIC ARTICLES WHILE PERIODICALLY ADAPTING DETECTIONTHRESHOLD, which is assigned to the assignee of the present invention.

Another type of proximity detector, sometimes referred to as aslope-activated or a peak-referenced detector (also referred to hereinas a peak detector) is described in U.S. Pat. No. 6,091,239 entitledDETECTION OF PASSING MAGNETIC ARTICLES WITH A PEAK-REFERENCED THRESHOLDDETECTOR, which is assigned to the assignee of the present invention.Another such peak-referenced proximity detector is described in U.S.Pat. No. 6,693,419 entitled PROXIMITY DETECTOR, which is assigned to theassignee of the present invention. In the peak-referenced proximitydetector, the threshold signal differs from the positive and negativepeaks (i.e., the peaks and valleys) of the magnetic field signal by apredetermined amount. Thus, in this type of proximity detector, theoutput signal changes state when the magnetic field signal comes awayfrom a peak or valley by the predetermined amount.

In order to accurately detect the proximity of the ferrous object, theproximity detector must be capable of closely tracking the magneticfield signal. Typically, one or more digital-to-analog converters (DACs)are used to generate a DAC signal, which tracks the magnetic fieldsignal. For example, in the above-referenced U.S. Pat. Nos. 5,917,320and 6,091,239, two DACs are used; one to track the positive peaks of themagnetic field signal (PDAC) and the other to track the negative peaksof the magnetic field signal (NDAC). And in the above-referenced U.S.Pat. No. 6,693,419, a single DAC tracks both the positive and negativepeaks of the magnetic field signal.

The magnetic field associated with the ferrous object and the resultingmagnetic field signal are proportional to the distance between theferrous object, for example the rotating ferrous gear, and the magneticfield sensors, e.g., the Hall elements, used in the proximity detector.This distance is referred to herein as an “air gap.” As the air gapincreases, the magnetic field sensors tend to experience a smallermagnetic field from the rotating ferrous gear, and therefore smallerchanges in the magnetic field generated by passing teeth of the rotatingferrous gear.

Proximity detectors have been used in systems in which the ferrousobject (e.g., the rotating ferrous gear) not only rotates, but alsovibrates. For the ferrous gear capable of unidirectional rotation aboutan axis of rotation in normal operation, the vibration can have at leasttwo vibration components. A first vibration component corresponds to a“rotational vibration,” for which the ferrous gear vibrates back andforth about its axis of rotation. A second vibration componentcorresponds to “translational vibration,” for which the above-describedair gap dimension vibrates. The rotational vibration and thetranslational vibration can occur even when the ferrous gear is nototherwise rotating in normal operation. Both the first and the secondvibration components, separately or in combination, can generate anoutput signal from the proximity detector that indicates rotation of theferrous gear even when the ferrous gear is not rotating in normaloperation.

Proximity detectors have been applied to automobile antilock brakesystems (ABS) to determine rotational speed of automobile wheels.Proximity detectors have also been applied to automobile transmissionsto determine rotating speed of transmission gears in order to shift thetransmission at predetermined shift points and to perform otherautomobile system functions.

Magnetic field signals generated by the magnetic field sensors duringvibration can have characteristics that depend upon the nature of thevibration. For example, when used in an automobile transmission, duringstarting of the automobile engine, the proximity detector primarilytends to experience rotational vibration, which tends to generatemagnetic field signals having a first wave shape. In contrast, duringengine idle, the proximity detector primarily tends to experiencetranslational vibration, which tends to generate magnetic field signalshaving a second wave shape. The magnetic field signals generated duringa vibration can also change from time to time, or from application toapplication, e.g., from automobile model to automobile model.

It will be understood that many mechanical assemblies have size andposition manufacturing tolerances. For example, when the proximitydetector is used in an assembly, the air gap can have manufacturingtolerances that result in variation in magnetic field sensed by themagnetic field sensors used in the proximity detector when the ferrousobject is rotating in normal operation and a corresponding variation inthe magnetic field signal. It will also be understood that the air gapcan change over time as wear occurs in the mechanical assembly.

Some conventional proximity detectors perform an automatic calibrationto properly operate in the presence of manufacturing tolerancevariations described above. Calibration can be performed on the magneticfield signal in order to maintain an AC amplitude and a DC offsetvoltage within a desired range.

Many of the characteristics of a magnetic field signal generated inresponse to a vibration can be the same as or similar to characteristicsof a magnetic field signal generated during rotation of the ferrousobject in normal operation. For example, the frequency of a magneticfield signal generated during vibration can be the same as or similar tothe frequency of a magnetic field signal generated during rotation innormal operation. As another example, the amplitude of a magnetic fieldsignal generated in response to a vibration can be similar to theamplitude of a magnetic field signal generated during a rotation innormal operation. Therefore, the conventional proximity detectorgenerates an output signal both in response to a vibration and inresponse to a rotation in normal operation. The output signal from theproximity detector can, therefore, appear the same, whether generated inresponse to a vibration or in response to a rotation in normaloperation.

It may be adverse to the operation of a system, for example, anautomobile system in which the proximity detector is used, for thesystem to interpret an output signal from the proximity detector to beassociated with a rotation in normal operation when only a vibration ispresent. For example, an antilock brake system using a proximitydetector to detect wheel rotation may interpret an output signal fromthe proximity detector to indicate a rotation of a wheel, when theoutput signal may be due only to a vibration. Therefore, the antilockbrake system might not operate as intended.

It may also be undesirable to perform the above-described proximitydetector calibration in response to a vibration rather than in responseto a rotation in normal operation. Since the conventional proximitydetector cannot distinguish a magnetic field signal generated inresponse to a rotation in normal operation from a magnetic field signalgenerated in response to a vibration, the proximity detector may performcalibrations at undesirable times when experiencing the vibration, andtherefore, result in inaccurate calibration.

SUMMARY OF THE INVENTION

The present invention provides methods and apparatus for detecting avibration of an object adapted to rotate in normal operation.

In accordance with the present invention, an apparatus for detecting avibration in an object adapted to rotate includes a plurality ofmagnetic field sensors for generating an RDIFF signal proportional to amagnetic field at a first location relative to the object and an LDIFFsignal proportional to a magnetic field at a second location relative tothe object. The apparatus also includes at least two rotation detectors(also referred to alternatively as proximity detectors), one of which iscoupled to at least one of the magnetic field sensors and is responsiveto the RDIFF signal to provide a first output signal indicative ofrotation of the object and the second one of which is also coupled to atleast one of the magnetic field sensors and is responsive to the LDIFFsignal to provide a second output signal indicative of rotation of theobject. A vibration processor is responsive to the first and secondoutput signals from the at least two rotation detectors for detectingthe vibration of the object.

In one embodiment, the vibration processor includes at least one of adirection-change processor, a phase-overlap processor, and adirection-agreement processor. The direction-change processor is coupledto at least one of the rotation detectors to detect the vibration of theobject in response to a change in the direction of rotation of theobject as indicated by the output signal of the at least one rotationdetector and to generate a direction-change output signal in response tothe vibration. The phase-overlap processor identifies a first signalregion associated with the RDIFF signal and a second signal regionassociated with the LDIFF signal, identifies an overlap of the firstsignal region and the second signal region, and generates aphase-overlap output signal in response to the overlap. Thedirection-agreement processor is coupled to the at least two rotationdetectors to detect the vibration of the object in response to adisagreement in the direction of rotation of the object as indicated byoutput signals of the at least two rotation detectors and to generate adirection-agreement output signal in response to the vibration.

In accordance with yet another aspect of the present invention, a methodfor detecting a vibration in an object adapted to rotate includesproviding a first output signal indicative of a rotation of the objectwith a first rotation detector, providing a second output signalindicative of the rotation of the object with a second rotationdetector, detecting a change in direction of rotation of the object fromthe first and the second output signals, and generating adirection-change output signal in response to the change in direction

In one particular embodiment, the method can also include providing athird output signal indicative of the rotation of the object with athird rotation detector, providing a fourth output signal indicative ofthe rotation of the object with a fourth rotation detector, detecting afirst direction of rotation of the object with the first rotationdetector and with the second rotation detector, detecting a seconddirection of rotation of the object with the third rotation detector andwith the fourth rotation detector, determining whether the firstdirection of rotation is the same as the second direction of rotation,and generating a direction-agreement output signal in response to thedetermination.

In yet another particular embodiment, the method can include detecting amagnetic field with a first magnetic field sensor at a first locationrelative to the object to provide an RDIFF signal, detecting a magneticfield with a second magnetic field sensor at a second location relativeto the object to provide an LDIFF signal, identifying a first signalregion associated with the RDIFF signal and a second signal regionassociated with the LDIFF signal, identifying an overlap of the firstsignal region and the second signal region, and generating aphase-overlap output signal in response to the overlap.

In accordance with yet another aspect of the present invention, thevibration processor includes a running mode processor and at least oneof the direction-change processor, the phase-overlap processor, and thedirection-agreement processor. The running-mode processor is coupled tothe rotation detectors to detect the vibration of the object in responseto an unresponsive one of the first and second output signals from arespective one of the first and second rotation detectors and togenerate a running-mode-vibration output signal indicative of thevibration.

In accordance with yet another aspect of the present invention, a methodfor detecting a vibration in an object adapted to rotate includesproviding a first output signal indicative of a rotation of the objectwith a first rotation detector and providing a second output signalindicative of the rotation of the object with a second rotationdetector. The method further includes detecting an unresponsive outputsignal from among the first and second output signals and generating arunning-mode-vibration output signal in response to the unresponsiveoutput signal.

With these particular arrangements, the apparatus and method candiscriminate a vibration from a rotation of the object.

In accordance with yet another aspect of the present invention, apeak-referenced detector for detecting rotation of an object adapted torotate includes a DIFF signal generator adapted to generate a DIFFsignal associated with a varying magnetic field generated by the objectwhen rotating. The peak-referenced detector also includes mean foridentifying a positive peak value corresponding to a positive peak ofthe DIFF signal, means for identifying a negative peak valuecorresponding to a negative peak of the DIFF signal, means forgenerating a first threshold as a first predetermined percentage belowthe positive peak value, and means for generating a second threshold asa second predetermined percentage above the negative peak value. Acomparator can be used for comparing the first and second thresholds tothe DIFF signal to generate an output signal indicative of the rotationof the object. In one particular embodiment, the first and secondpredetermined thresholds can each be about fifteen percent.

With this particular arrangement, the peak-referenced detector can usethresholds that are predetermined percentages away from the positive andnegative peaks of the DIFF signal, unlike a conventional peak-referenceddetector that uses thresholds that are a predetermined value away fromthe positive and negative peaks of the DIFF signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention, as well as the invention itselfmay be more fully understood from the following detailed description ofthe drawings, in which:

FIG. 1 is a block diagram of a sensor containing a vibration processoraccording to the invention;

FIG. 2 is a block diagram showing rotation detectors that can be used inthe sensor of FIG. 1 in greater detail;

FIG. 2A shows a series of waveforms associated with the rotationdetectors of FIG. 2;

FIG. 2B is a block diagram of a circuit used to provide control signalsto the rotation detectors of FIG. 2;

FIGS. 3-3B show a series of waveforms including magnetic fields,corresponding output signals of magnetic field sensors, correspondingoutput signals associated with rotation detectors, and correspondingoutput signals associated with a direction-change processor of FIG. 1 inresponse to a vibration of an object;

FIG. 4-4B show a series of waveforms including magnetic fields,corresponding output signals of magnetic field sensors, correspondingoutput signals associated with rotation detectors, and correspondingoutput signals associated with the direction-change processor of FIG. 1in response to a rotation of the object in normal operation;

FIG. 5 shows a series of waveforms including magnetic fields,corresponding output signals associated with rotation detectors, andcorresponding output signals associated with a direction-agreementprocessor of FIG. 1 in response to the vibration of the object and inresponse to the rotation of the object in normal operation;

FIG. 6 is a graph showing magnetic fields associated with aphase-overlap processor of FIG. 1 in response to the rotation of theobject in normal operation;

FIG. 7 is a graph showing magnetic field signals and other signalsassociated with the phase-overlap processor of FIG. 1 in response to avibration;

FIG. 8 is a flow chart showing a process of generating adirection-change output signal associated with the direction-changeprocessor of FIG. 1;

FIGS. 8A and 8B together are a flow chart showing further details of theprocess of FIG. 8;

FIG. 9 is a flow chart showing a process of generating adirection-agreement output signal associated with thedirection-agreement processor of FIG. 1;

FIG. 10 is a flow chart showing a process of generating a phase-overlapoutput signal associated with the phase-overlap processor of FIG. 1;

FIG. 11 is a block diagram of an alternate sensor containing a vibrationprocessor according to the invention;

FIG. 12-12B show a series of waveforms including magnetic fields,corresponding output signals of magnetic field sensors, correspondingoutput signals associated with rotation detectors, and correspondingoutput signals associated with a running-mode processor of FIG. 11 inresponse to a vibration of an object;

FIG. 13 is a block diagram of a circuit that can be used to provide therunning-mode processor of FIG. 11;

FIG. 14 is a flow chart showing a process of generating arunning-mode-vibration output signal associated with the running-modeprocessor of FIGS. 11 and 13; and

FIG. 14A is a flow chart showing further detail associated with theprocess of FIG. 14.

DETAILED DESCRIPTION OF THE INVENTION

Before describing the present invention, some introductory concepts andterminology are explained. As used herein, the term “rotationalvibration” refers to a back and forth rotation of an object about anaxis of rotation, which object is adapted to rotate in a unidirectionalmanner about the axis of rotation in normal operation. As used herein,the term “translational vibration” refers to translation of the objectand/or of magnetic field sensors used to detect magnetic fieldsgenerated by the object generally in a direction perpendicular to theaxis of rotation. It should be recognized that both rotational vibrationand translational vibration can cause signals to be generated by themagnetic field sensors.

Referring now to FIG. 1, an exemplary sensor 10 includes a plurality ofmagnetic field sensors 14 a-14 c for generating an RDIFF signal 28proportional to a magnetic field at a first location relative to anobject 11 and an LDIFF signal 58 proportional to a magnetic field at asecond location relative to the object 11. As described more fullybelow, the first and second locations correspond to right and leftchannels. The object 11 can be an object adapted to rotate, for example,a ferrous gear, which, in addition to unidirectional rotation in normaloperation, is also subject to undesirable rotational and translationalvibrations. The sensor 10 includes a right channel amplifier 16providing the RDIFF signal 28 and a left channel amplifier 50 providingthe LDIFF signal 58.

The sensor 10 also includes rotation detectors 12, including at leasttwo rotation detectors as at least one of a right channel thresholddetector 22 and a right channel peak-referenced detector 20, and atleast one of a left channel threshold detector 56 and a left channelpeak-referenced detector 54.

The right channel threshold detector 22 is responsive to the RDIFFsignal 28 and provides a first output signal 26 (RThreshOut) indicativeof a rotation of the object. The left channel threshold detector 56 isresponsive to the LDIFF signal 58 and provides a second output signal 62(LThreshOut) also indicative of the rotation of the object. The rightchannel peak-referenced detector 20 is responsive to the RDIFF signal 28and provides a third output signal 24 (RPeakOut) further indicative ofthe rotation of the object. The left channel peak-referenced detector 54is responsive to the LDIFF signal 58 and provides a fourth output signal62 (LThreshOut) still further indicative of the rotation of the object.

The designations “left” and “right” (also L and R, respectively) areindicative of physical placement of the magnetic field sensors 14 a-14 crelative to the object 11 and correspond to left and right channels,where a channel contains the signal processing circuitry associated withthe respective magnetic field sensor(s). For example, the magnetic fieldsensors 14 a, 14 b differentially sense the magnetic field at a locationto the right of the object 11 and the right channel contains circuitryfor processing the magnetic field thus sensed (e.g., right channelamplifier 16, R Peak-referenced detector 20, and R threshold detector22). In the illustrative embodiment, three magnetic field sensors areused for differential magnetic field sensing, with the central sensor 14b used in both channels. While three magnetic field sensors 14 a-14 care shown, it should be appreciated that two or more magnetic fieldsensors can be used with this invention. For example, in an embodimentusing only two magnetic field sensors 14 a, 14 b, magnetic field sensor14 a can be coupled to the right channel amplifier 16 and magnetic fieldsensor 14 b can be coupled to the left channel amplifier 50. The rightchannel includes magnetic field sensors 14 a and 14 b, the right channelamplifier 16, the right channel peak-referenced detector 20, and theright channel threshold detector 22. The left channel includes magneticfield sensors 14 b and 14 c the left channel amplifier 50, the leftchannel peak-referenced detector 54, and the left channel thresholddetector 56. It will be appreciated that right and left are relativeterms, and, if reversed, merely result a relative phase change in themagnetic field signals. This will become more apparent below inconjunction with FIGS. 8A and 8B.

The sensor 10 also includes a vibration processor 13 responsive tooutput signals from at least two rotation detectors 20, 22, 54, 56 fordetecting the vibration of the object. The vibration processor 13includes at least one of a peak direction-change processor 30, athreshold direction-change processor 36, a direction-agreement processor40, and a phase-overlap processor 46. In one particular embodiment, thevibration processor 13 contains the threshold direction-change processor36, the direction-agreement processor 40, and the phase-overlapprocessor 46.

The threshold direction-change processor 36 is described in greaterdetail in conjunction with FIGS. 3-4B, the peak direction-changeprocessor 30 and the threshold direction-change processor 36 aredescribed in greater detail in conjunction with FIGS. 8 and 8A, thedirection-agreement processor 40 is described in greater detail inconjunction with FIGS. 5 and 9, and the phase-overlap processor 46 isdescribed in greater detail in conjunction with FIGS. 6, 7, and 10.However, let it suffice here to say that the peak direction-changeprocessor 30 and the threshold direction-change processor 36 detect thevibration of the object and generate respective direction-change outputsignals 32, 38 in response to the vibration. The direction-agreementprocessor 40 detects the vibration of the object and generates adirection-agreement output signal 42 in response to the vibration. Thephase-overlap processor 46 also detects the vibration of the object andgenerates a phase-overlap output signal 48 in response to the vibration.

A combining processor 34 logically combines at least two of thedirection-change output signal 38, the second direction-change outputsignal 32, the direction-agreement output signal 42, and thephase-overlap output signal 48 to provide a vibration-decision outputsignal 80 indicative of whether or not the object is vibrating. Forexample, in one particular embodiment, the logical combining is an ORfunction providing that if any of the direction-change output signal 38,the direction-change output signal 32, the direction-agreement outputsignal 42, and the phase-overlap output signal 48 indicates a vibrationof the object, then the vibration-decision output signal 80 indicatesthe vibration accordingly, for example, as a high logic state.

However, in an alternate arrangement, the sensor 10, has one vibrationprocessor, selected from among the peak-direction change processor 30,the threshold direction-change processor 36, the direction-agreementprocessor 40, and the phase-overlap processor 46, the selected one ofwhich provides the vibration decision output signal 80.

It will become apparent from discussion below that the thresholddirection-change processor 38, the peak direction-change processor 30,the direction-agreement processor 40, and the phase-overlap processor 46can detect rotational vibration of the rotating object, for example, therotating ferrous gear described above. It will also be apparent that thephase-overlap processor 46 can detect translational vibration of theobject and/or of the magnetic field sensors 14 a-14 c. However, in otherembodiments, any of the above-identified processors can be adapted todetect either the rotational vibration or the translational vibration orboth.

The exemplary sensor 10 can also include a speed detector 64 to detect arotational speed of the object and provide a corresponding speed outputsignal 66 indicative of a speed of rotation of the object, a directiondetector 68 to detect a direction of rotation of the object and providea corresponding direction output signal 70 indicative of the directionof rotation of the object, an air gap detector 72 to detect an air gapbetween one or more of the magnetic field sensors 14 a-14 c and theferrous object and provide a corresponding air gap output signal 74indicative of the air gap, and a temperature detector 76 to detect atemperature and provide a corresponding temperature output signal 78indicative of the temperature.

An output protocol processor 82 is responsive to one or more of theoutput signals 66, 70, 74, 78 and to the vibration-decision outputsignal 80 for generating a sensor output signal 84 in accordance withthe received signals. In one particular embodiment, for example, theoutput signal 84 has a first characteristic when the vibration-decisionoutput signal 80 indicates a vibration, and a second characteristic whenthe vibration-decision output signal 80 indicates no vibration. Forexample, in one particular embodiment, the output signal 84 can bestatic (i.e., statically high or low) when the vibration-decision outputsignal 80 indicates the vibration, and can be active (e.g., an ACwaveform having a frequency proportional to the speed output signal 66)when the vibration-decision output signal 80 indicates no vibration. Inother embodiments, the output protocol processor 82 provides an encodedoutput signal 84 in accordance with one of more or output signals 66,70, 74, 78, 80.

Referring now to FIG. 2, exemplary rotation detectors 102, whichcorrespond to the rotation detectors 12 of FIG. 1, are shown in greaterdetail. A right channel corresponds to an upper half of FIG. 2 and aleft channel corresponds to a lower half of FIG. 2. It will beappreciated that the left channel has characteristics similar to theright channel. For simplicity, only the right channel is describedherein.

An input signal 104 from a right channel amplifier, e.g., the rightchannel amplifier 16 of FIG. 1, can include an undesirable DC offset. Aright channel auto offset controller 106, a right channel offsetdigital-to-analog converter (DAC) 108 and a summer 110 are provided inorder to eliminate the DC offset by known techniques. A right channelautomatic gain controller (RAGC) 114 provides an RDIFF signal 136 havingan amplitude within a predetermined amplitude range. Control of the RAGC114 is further described below. It should be understood that the RDIFFsignal 136 is representative of the magnetic field experienced by one ormore magnetic field sensors, for example, the magnetic field sensors 14a, 14 b of FIG. 1.

The RDIFF signal 136 is provided to a right channel peak (RPeak)comparator 116 and to a right channel threshold (RThresh) comparator138. The RPeak comparator 116 also receives a threshold voltage 134 andthe RThresh comparator 138 receives a threshold voltage 135. Generationof the threshold voltages 134, 135 is further described in conjunctionwith FIGS. 2A and 2B.

The threshold voltage 134 switches between two values, a first one ofwhich is a first predetermined percentage below a positive peak of theRDIFF signal 136 and a second one of which is a second predeterminedpercentage above a negative peak of the RDIFF signal 136. In oneparticular embodiment, the first and second predetermined percentagesare each about fifteen percent. The first threshold voltage 134 is,therefore, relatively near to and below a positive peak of the RDIFFsignal 136 or relatively near to and above a negative peak of the RDIFFsignal 136. Therefore, the RPeak comparator 116 generates an RPeakOutsignal 118 having edges closely associated with the positive andnegative peaks of the RDIFF signal 136.

The threshold voltage 135 also switches between two values, a first oneof which is a first predetermined percentage of the peak-to-peakamplitude of the RDIFF signal 136 and a second one of which is a secondpredetermined percentage of the peak-to-peak amplitude of the RDIFFsignal 136. In one particular embodiment, the first predeterminedpercentage is about sixty percent and the second predeterminedpercentage is about forty percent of the peak-to-peak amplitude of theRDIFF signal 136. Therefore, the RThresh comparator 138 generates anRThreshOut signal 140 having edges relatively closely associated withthe midpoint, or fifty percent point, between the positive peak and thenegative peak of the RDIFF signal 136.

The threshold voltages 134, 135 are generated by counters 124, 125,logic circuits 123, 127, a right channel PDAC 126, a right channel NDAC128, comparators 122, 130, a resistor ladder 132 and transmission gates133 a-133 d. The comparator 122 receives the RDIFF signal 136 and anoutput from the right channel PDAC 126, and, by way of feedback providedby the logic circuit 123 and the counter 124, causes the output of thePDAC 126 (i.e., the PDAC voltage) to track and hold the positive peaksof the RDIFF signal 136. Similarly, the comparator 130 receives theRDIFF signal 136 and an output from the right channel NDAC 128, and, byway of feedback provided by the logic 127 and the counter 125, causesthe output of the NDAC 128 (i.e., the NDAC voltage) to track and holdthe negative peaks of the RDIFF signal 136. Therefore, the differentialvoltage between the output of the PDAC 126 and the output of the NDAC128 represents the peak-to-peak amplitude of the RDIFF signal 136. Theoutputs of the PDAC 126 and the NDAC 128 are described below in greaterdetail in conjunction with FIG. 2A.

The PDAC and NDAC voltages are provided to opposite ends of the resistorladder 132. The transmission gates 133 a, 133 d provide the thresholdvoltage 134 as one of two voltage values as described above, dependingupon the control voltages RPeakHyst and its inverse RPeakHystN appliedto the transmission gates 133 a, 133 d respectively. Similarly, thetransmission gates 133 b, 133 c provide the threshold 135 voltage as oneof two voltage values as described above, depending upon the controlvoltages RThreshOut 140 and its inverse RThreshOutN applied to thetransmission gates 133 c, 133 b respectively.

It should be recognized from the discussion above that the two states ofthe threshold voltage 134 are closely associated with the positive peakand the negative peak of the RDIFF signal 136, while the two states ofthe threshold 135 are closely associated with a midpoint of the RDIFFsignal 136. This difference is accomplished by way of the controlsignals applied to the transmission gates 133 a, 133 d compared tocontrol signals applied to the transmission gates 133 b, 133 c. Thecontrol signals are further described below in conjunction with FIGS. 2Aand 2B.

A shared AGC DAC 152 is shown in the lower half of FIG. 2, providing ashared AGC DAC output signal 154 to control the gain of both the RAGC114 and LAGC 156 amplifiers. The shared AGC DAC output signal 154 causesboth the right and the left channels to have the same gain. One ofordinary skill in the art will understand how to set the shared AGC DAC152 to provide and appropriate shared AGC DAC output signal 154.

Referring now to FIG. 2A, an RDIFF signal 186 can correspond, forexample to the RDIFF signal 28 of FIG. 1 and the RDIFF signal 136 ofFIG. 2. The RDIFF signal 186 is shown to have a shape of a simple sinewave for clarity. However, it will be recognized that the RDIFF signal186 can have various shapes.

Two fill cycles of the RDIFF signal 186 are shown, however,relationships of the RDIFF signal 186 to other waveforms is describedbeginning at a point 186 a. The point 186 a and another point 186 n eachcorrespond to negative peaks of the RDIFF signal 186. Points 186 b, 186m, 186 p each correspond to the RDIFF signal 186 having reached aboutfifteen percent of its peak-to-peak amplitude. Points 186 c, 186 j, 186q each correspond to the RDIFF signal 186 having reached about fortypercent of its peak-to-peak amplitude. Points 186 d, 186 i, 186 r eachcorrespond to the RDIFF signal 186 having reached about sixty percent ofits peak-to-peak amplitude. Points 186 f, 186 h each correspond to theRDIFF signal 186 having reached about eighty five percent of itspeak-to-peak amplitude. While particular percentages are describedabove, other percentages can also be used. However, the points 186 b,186 e, 186 h, 186 k, and 186 p will be seen to be associated with apeak-referenced detector, and therefore, are selected to be relativelynear to a positive of a negative peak of the RDIFF signal 186.

A PDAC signal 184 corresponds to the PDAC output signal label in FIG. 2and an NDAC signal 185 corresponds to the NDAC output signal label inFIG. 2. As seen in FIG. 2, the PDAC and NDAC output signals are appliedto the resistor ladder 132, which can provide outputs at a variety ofpercentages of a difference between the PDAC output signal 184 and theNDAC output signal 185.

Presuming steady state conditions, at a time associated with the point186 a, the PDAC output signal 184 is at a steady state relatively highlevel corresponding to a positive peak of the RDIFF signal 186, where itremains until a time associated with the point 186 d, corresponding to asixty percent level. At this time, the PDAC output signal 184 countsdown until the PDAC output signal 184 intersects the RDIFF signal 186 atthe point 186 e, at which point, the PDAC output signal 184 reversesdirection and counts up to track the RDIFF signal 186 to its nextpositive peak at the point 186 g. Upon reaching the point 186 g, thePDAC output signal 184 again holds its value at the positive peak of theRDIFF signal 186.

At the point 186 a, the NDAC output signal 185 is at a steady staterelatively low level corresponding to a negative peak of the RDIFFsignal 186, where it remains until a time associated with the point 186j, corresponding to a forty percent level. At this time, the NDAC outputsignal 185 counts up until the NDAC output signal 185 intersects theRDIFF signal 186 at the point 186 k, at which point, the NDAC outputsignal 185 reverses direction and counts down to track the RDIFF signal186 to its next negative peak at the point 186 n. Upon reaching thepoint 186 n, the NDAC output signal 185 again holds its value at thenegative peak of the RDIFF signal 186. The above-described behavior ofthe PDAC signal 184 and the NDAC signal 185 repeats on each cycle of theRDIFF signal 186.

An RThreshOut signal 187 corresponds to the RThreshOut signal 26 of FIG.1 and the RThreshOut signal 140 of FIG. 2. The RThreshOut signal 187 isa digital signal that, due to transitions of a threshold signal 188described below, switches states at times corresponding to points 186 d(sixty percent), 186 j (forty percent), and 186 r (sixty percent).

In order to achieve the desired edge time placement of the RThreshOutsignal 187, a threshold signal 188 is generated, for example, thethreshold signal 135 of FIG. 2 with the ladder network 132 of FIG. 2. Asshown in FIG. 2 and as will be understood from the waveforms 184, 185,186, 187, of FIG. 2A, using the RThreshOut signal 187 (140, FIG. 2) tocontrol the transmission gate 133 c of FIG. 2 and its inverse to controlthe transmission gate 133 b, results in the threshold signal 188 (signal135, FIG. 2). The resistor ladder 132 of FIG. 2 is scaled to providetransitions of the threshold 188 (signal 135, FIG. 2) between levels atabout forty percent and about sixty percent of the peak-to-peakamplitude of the RDIFF signal 186 (signal 136, FIG. 2).

Taking edge 187 a as representative of a positive edge in the RThreshOutsignal 187 occurring at a time associated a the sixty percent point,e.g., the point 186 d, it can be seen that the edge 187 a is generallycoincident with the downward edge 188 a of the threshold signal 188. Itwill be understood that the transition 188 a of the threshold 188 actsto provide hysteresis, for example, to the comparator 138 of FIG. 2.Following the edges 187 a, 188 a, which occur at the sixty percent pointof the RDIFF signal 186, the next desired switch point is at the fortypercent level of the RDIFF signal 186. Following the edges 187 a, 188 a,a switch point at the forty percent level does not occur until a timecorresponding to the point 186 j, where the RThreshOut signal 187 hastransition 187 b and the threshold signal 188 has transition 188 b,again providing hysteresis.

It should be apparent that waveforms 187, 188 apply to a thresholddetector, for example, a threshold detector associated with the RThreshcomparator 138 of FIG. 2. Similar waveforms apply to a peak-referenceddetector, for example a peak-referenced detector associated with theRPeak comparator 116 of FIG. 2. However, in order to generate anRPeakOut signal 189, different thresholds and timing are applied. TheRPeakOut signal 189 corresponds, for example to the RPeakOut signal 24of FIG. 1 and the RPeakOut signal 118 of FIG. 2. The RPeakOut signal 189has an edge 189 a associated with a point 186 b at a fifteen percentlevel of the RDIFF signal and an edge 189 b associated with a point 186b at an eight-five percent level of the RDIFF signal 138.

In order to achieve the desired edge time placement of the RPeakOutsignal 189, a threshold signal 190 is generated, which corresponds, forexample, to the threshold signal 134 of FIG. 2. As shown in FIG. 2 andas will be understood from the waveforms 184, 185, 186, 189, of FIG. 2A,the RPeakOut signal 190 (118, FIG. 2) is not used to directly controlthe transmission gates 133 a, 133 d of FIG. 2 to generate the thresholdsignal 190 (134, FIG. 2). This can be seen merely by the phasedifference between the threshold signal 190 and the RPeakOut signal 189.

If the RPeakOut signal 189 were directly used to control thetransmission gates 133 a, 133 b of FIG. 2, the threshold signal 190would not behave as desired. For example, if the edge 189 a at a timeassociated with the point 186 b (a fifteen percent point) were used togenerate a transition in the threshold 190, then the next eighty-fivepercent point 186 f would be detected by the RPeak comparator 116 (FIG.2). This is not the desired detection point. Instead it is desired thatthe point 186 h be detected next, which is also an eighty-five percentpoint. It is desired that the eighty-five percent point be fifteenpercent below and after the positive peak of the RDIFF signal 186occurring at point 186 g, as it is also desired that the fifteen percentpoint 186 b be fifteen percent above and after the negative peakoccurring at point 186 a.

To generate the RPeakOut signal 189 having transitions associated withthe proper fifteen percent and eighty-five percent points of the RDIFFwaveform 186, for example, having the edges 189 a, 189 b associated withthe points 186 b, 186 h, the threshold signal 190 has edges that do notalign with the edges 189 a, 189 b of the RPeakOut signal 189. In oneparticular embodiment, the edges 190 a, 190 b align instead with thepoints 186 e, 186 k of the RDIFF signal 186. As described above, thepoint 186 e corresponds to the point at which the PDAC output signal 184intersect the RDIFF signal 186 as shown, and the point 186 k correspondsto the point at which the NDAC output signal 185 intersects the RDIFFsignal 186.

In order to generate the transitions 190 a, 190 b in the threshold 190,a control signal RPeakHyst (see FIG. 2) is generated to control thetransmission gates 133 a, 133 d, having edges generally at the sametimes as the edges 190 a, 190 b. Generation of the RPeakHyst controlsignal is described in conjunction with FIG. 2B.

Referring now to FIG. 2B, a circuit can be used to provide the RPeakHystsignal described above in conjunction with FIG. 2A. As described above,the points 186 e, 186 k (FIG. 2A) are detected as the intersection ofthe PDAC signal 184 and the NDAC signal 185 respectively with the RDIFFsignal 186. The detections can be accomplished with comparators 191, 192to provide intermediate signals COMP_N and COMP_P, which are provided asinputs along with the RThreshOut signal (e.g., 140, FIG. 2, 187, FIG.2A) to AND gates 194, 195. Outputs of the AND gates 194, 195 are used tocontrol a set/reset flip-flop 196, generating the RPeakHyst signal 198.An inverter 197 can be used to provide an inverted signal RPeakHystN.The RPeakHyst and RPeakHystN signals 198, 199 have edges coincident withthe edges 190 a, 190 b of the threshold signal 190 (FIG. 2A), and areused to control the transmission gates 133 a, 133 d respectively of FIG.2.

From the above description, it should be apparent that thepeak-referenced detectors (e.g., 20, 54 of FIG. 1) differ fromconventional peak-referenced detectors in that, whereas conventionalpeak-referenced detectors use thresholds that are a fixed voltage abovethe negative peak of a DIFF signal and a fixed voltage below thepositive peak of the DIFF signal, the peak-referenced detector describedabove uses thresholds that are a percentage above the negative peak ofthe DIFF signal and a percentage below a positive peak or the DIFFsignal.

While FIGS. 2A and 2B describe a peak-referenced detector usingthresholds that are different than thresholds used in a conventionalpeak-referenced detector, in other embodiments, conventionalpeak-referenced detectors can be used with this invention. For example,the peak-referenced detectors 20, 54 can be conventional peak-referenceddetectors using thresholds that are a fixed voltage above negative peaksof the RDIFF signals 28, 58 respectively and a fixed voltage belowpositive peaks of the RDIFF signals 28, 58.

Referring now to FIGS. 3-3B, waveforms are shown which are associatedwith the threshold direction-change processor 36 of FIG. 1 in responseto a rotational vibration. However, the waveforms can also be associatedwith the peak direction-change processor 30 of FIG. 1.

Referring first to FIG. 3, waveforms 202 and 204, shown by phantomlines, represent magnetic fields experienced by the sensor 10 of FIG. 1if the sensor 10 were in proximity, for example, to a rotating ferrousgear continuously rotating in normal operation. Portions 202 a, 204 a ofthe magnetic field signals 202, 204, however, are representative ofmagnetic fields that would be experienced by the sensor 10 in responseto a rotational vibration of the ferrous gear. More particularly, themagnetic field signal 202 a is representative of the magnetic fieldexperienced by the magnetic field sensors 14 a, 14 b (FIG. 1) and themagnetic field signal 204 a is representative of the magnetic fieldexperienced by the magnetic field sensors 14 b, 14 c (FIG. 1) inresponse to the rotational vibration.

A complete cycle of the magnetic fields 202, 204 corresponds to onetooth of the ferrous gear passing by the sensor 10, which generallycorresponds to only a small portion of a complete revolution of theferrous gear. The magnetic field signals 202 a and 204 a associated withthe rotational vibration are bounded by a region between phases φ1 andφ2. The region between phases φ1 and φ2, therefore, corresponds to aneven smaller portion of a complete rotation of the ferrous gear.

While shown in one position on a time scale, the region between phasesφ1 and φ2 can be at any position on the time scale. Furthermore, it willbe appreciated that the phases φ1 and φ2 can have any separation. Alarger separation corresponds to a larger magnitude rotational vibrationand a smaller separation corresponds to a smaller magnitude rotationalvibration.

While the magnetic fields 202, 204 have a frequency associated with therotation of the ferrous gear in normal operation, it should beappreciated that the magnetic fields 202 a, 204 a can be experienced atany frequency by the sensor 10 (FIG. 1), determined by a rate ofrotational vibration. The ferrous gear rotating back and forth about itsaxis of rotation causes the sensor 10 to experience the magnetic fields202 a, 204 a at the frequency of the rotational vibration.

Referring now to FIG. 3A, the sensor 10 generates an LDIFF signal 206and an RDIFF signal 208. The LDIFF signal 206 corresponds, for example,to the LDIFF signals 58, 158 shown in FIGS. 1 and 2 respectively, andthe RDIFF signal 208, corresponds, for example, to the RDIFF signals 28,136 of FIGS. 1 and 2 respectively. It will be apparent from the magneticfields 202 a, 204 a shown in FIG. 3, that the LDIFF signal 206 can havea greater magnitude than the RDIFF signal 208. However if the regionbounded by φ1 and φ2 (FIG. 3) were to be at a different position alongthe time scale in FIG. 3, it is equally possible for the LDIFF signal206 and the RDIFF signal 208 to have other magnitude relationships. Inresponse to a vibration, the LDIFF signal 206 and the RDIFF signal 208are approximately in phase.

The LDIFF signal 206 and the RDIFF signal 208 can have different waveshapes depending, for example, on slopes in the region bounded by φ1 andφ2 of FIG. 3, and on the nature of the vibration. As shown, the LDIFFsignal 206 has a substantially triangular shape whereas the RDIFF signal208 has a substantially sinusoidal shape.

Furthermore, as described above, the region bounded by φ1 and φ2 (FIG.3) can be at any position and have any separation relative to themagnetic field signals 202, 204. Furthermore, the rotational vibrationassociated with the region bounded by φ1 and φ2 can have any type ofmovement. Therefore, it should be recognized that the LDIFF signal 206and the RDIFF signal 208 can be more complex waveforms than those shown.

In operation, the LDIFF signal 206 is compared to thresholds th1 and th2and the RDIFF signal 208 and is compared to thresholds th3 and th4. Thethresholds th1, th2 correspond to two states of the threshold 135 ofFIG. 2 and the thresholds th3, th4 correspond to two states of athreshold 178 of FIG. 2.

Referring now to FIG. 3B, comparison of the LDIFF signal to thethresholds th1 and th2 shown in FIG. 3A results in an LThreshOut signal210 and comparison of the RDIFF signal 208 to the thresholds th3 and th4of FIG. 3A results in an RThreshOut signal 216. The LThreshOut signal210 corresponds to the LThreshOut signals 62, 182 of FIGS. 1 and 2respectively and the RThreshOut signal 216 corresponds to the RThreshOutsignal 26, 140 of FIGS. 1 and 2 respectively. Because the LDIFF signal206 is larger than and has a different shape than the RDIFF signal 208,the LThreshOut signal 210 has a positive state duty cycle less than theRThreshOut signal 216.

As described above, in an alternate embodiment, the signals of FIGS.3-3B can be associated with the peak-referenced detectors 20, 54 of FIG.1, in which case, the thresholds th1-th4 are selected in accordance withthe left channel peak-referenced detector 54 and the right channelpeak-referenced detector 20 of FIG. 1, and the LThreshOut signal 210 andan RThreshOut signal 216 are instead an LPeakOut signal (not shown) andan RPeakOut signal (not shown) corresponding to the LPeakOut signal 60,162 and an RPeakOut signal 24, 116 of FIGS. 1 and 2 respectively.

The LThreshOut signal 210 has rising edges 212 a-212 d and falling edges214 a-214 d and the RThreshOut signal 216 has rising edges 218 a-218 dand falling edges 220 a-220 d. In operation, the thresholddirection-change processor 36 (FIG. 1) compares the LThreshOut signal210 to the RThreshOut signal 216 to detect leading rising and leadingfalling edges. Detection of the leading rising and falling edges of theLThreshOut signal 210 and the RThreshOut signal 216 results in adirection output signal 221 having a state indicative of a direction ofrotation. For example, the falling edge 220 a of the right channel leadsthe falling edge 214 a of the left channel, resulting in a high level inthe direction output signal 221. Also, the rising edge 218 b of theright channel lags the rising edge 212 b of the left channel, resultingin a low level in the direction output signal 221. A leading edge in theLThreshOut signal 214 results in a first logic state of the directionoutput signal 221, and a leading edge in the RThreshOut signal 216results in an opposite logic state. Therefore, in response to rotationalvibration of the ferrous gear, the direction output signal 221 changesstate. A direction-change output signal 222 can be generated to providea pulse at each edge of the direction output signal 221. Generation ofthe direction-change output signal 222 is further described inconjunction with FIGS. 8 and 8A.

The direction-change output signal 222 corresponds either to thedirection-change output signal 38 of FIG. 1 or the to thedirection-change output signal 32 of FIG. 1, depending upon whether thethresholds th1-th4 are selected in accordance with the thresholddetectors 22, 56 of FIG. 1, or with the peak reference detectors 20, 54of FIG. 1. It will become more apparent from the discussion below inconjunction with FIGS. 4-4B that a direction-change output signal 222that changes state as shown is indicative of a rotational vibration anda direction-change output signal 222 that does not change state isindicative of no rotation direction change, i.e., of a unidirectionalrotation in normal operation. Therefore, a vibration can be detected.

It should be recognized that the waveforms shown in FIG. 3-3C representone example of possible waveforms associated with a vibration. Forexample, other waveforms can be shown to occur in the presence of avibration for which the LDIFF signal 206 and the RDIFF signal 208 areclosely matched in shape and amplitude, which in turn results in theLThreshOut signal 210 and the RThreshOut signal 216 being closelymatched. However, even in this case, due to electrical noise present onthe LDIFF and RDIFF signals 206, 208, the LThreshOut signal 210 and theRThreshOut signal 216 can have leading edges that jitter in timeresulting in a toggling direction-change output signal 222 and detectionof the vibration. However, it is also possible that the LDIFF signal 206and the RDIFF signal 210 can have waveform shapes resulting in nodetection of a vibration. In this case, any one of the other vibrationdetectors 30, 36, 40, and 46 (FIG. 1) can detect the vibration.

Referring now to FIGS. 4-4B in which like elements of FIGS. 3-3B areshown having like reference designations, waveforms are shown that areassociated with the threshold direction-change processor 36 of FIG. 1 inresponse to a rotation in normal operation. Referring first to FIG. 4,magnetic field signals 252 and 254 are representative of magnetic fieldsthat would be experienced by the sensor 10 of FIG. 1 if the sensor 10were in proximity, for example, to a rotating ferrous gear continuouslyrotating in one direction in normal operation. More particularly, themagnetic field signal 252 is representative of the magnetic fieldexperienced by the magnetic field sensors 14 a, 14 b (FIG. 1) and themagnetic field signal 254 is representative of the magnetic fieldexperienced by the magnetic field sensors 14 b, 14 c (FIG. 1) inresponse to the rotation in normal operation.

A complete cycle of the magnetic fields 252, 254 corresponds to onetooth of the ferrous gear passing by the sensor 10, which generallycorresponds to only a small portion of a complete revolution of theferrous gear.

Referring now to FIG. 4A, the sensor 10 generates an LDIFF signal 256and an RDIFF signal 258. The LDIFF signal 256 corresponds, for example,to the LDIFF signals 58, 158 shown in FIGS. 1 and 2 respectively, andthe RDIFF signal 258, corresponds, for example, to the RDIFF signals 28,136 of FIGS. 1 and 2 respectively. It will be apparent from the magneticfields 252, 254 shown in FIG. 4, that the LDIFF signal 256 has about thesame magnitude as the RDIFF signal 258.

The LDIFF signal 256 and the RDIFF signal 258 are out of phase by anamount proportional to a variety of factors, including but not limitedto a separation between gear teeth on the ferrous gear and a separationbetween the magnetic field sensors, i.e., a separation between themagnetic field sensors 14 a, 14 b (FIG. 1) and the magnetic fieldsensors 14 b, 14 c (FIG. 1). In one particular embodiment, the ferrousgear rotates at approximately 1000 rpm, has gear teeth that areseparated by approximately ten millimeters, and a center between themagnetic field sensors 14 a, 14 b is separated from a center between themagnetic field sensors 14 b, 14 c by approximately 1.5 millimeters. Withthis particular arrangement, the LDIFF signal 256 and the RDIFF signal258 differ in phase by approximately forty degrees.

As described above, in operation, thresholds th1 and th2 are applied tothe LDIFF signal 256 and thresholds th3 and th4 are applied to the RDIFFsignal 258. The thresholds th1-th4 are described above in conjunctionwith FIG. 3A.

Referring now to FIG. 4B, application of the thresholds th1-th4 shown inFIG. 4A result in an LThreshOut signal 260 and an RThreshOut signal 266.Because the LDIFF signal 256 is about the same magnitude as the RDIFFsignal 258 but at a different relative phase, the LThreshOut signal 260has a duty cycle similar to that of the RThreshOut signal 266, but atthe different relative phase.

The LThreshOut signal 260 has rising edges 262 a-262 b and falling edge264 a and the RThreshOut signal 266 has rising edges 268 a-268 b andfalling edge 270 a. In operation, the LThreshOut signal 260 is comparedby the threshold direction-change processor 36 (FIG. 1) to theRThreshOut signal 266 to detect leading rising and leading fallingedges. Detection of the leading rising and falling edges of theLThreshOut signal 260 and the RThreshOut signal 266 results in adirection output signal 271 indicative of a direction of rotation. Forexample, the falling edge 264 a of the left channel leads the fallingedge 270 a of the right channel, resulting in a low level in thedirection output signal 271. Also, the rising edge 262 b of the leftchannel leads the rising edge 268 b of the right channel, resultingagain in a low level in the direction output signal 271. Adirection-change output signal 272 can be generated to provide a pulseat each edge of the direction output signal 271. Therefore, in responseto rotation of the ferrous gear in normal operation, thedirection-change output signal 272 remains at one state.

The direction-change output signal 272 corresponds either to thedirection-change output signal 38 of FIG. 1 or the direction-changeoutput signal 32 of FIG. 1, depending upon whether the thresholdsth1-th4 are in accordance with the threshold detectors 22, 56 of FIG. 1,or with the peak-referenced detectors 20, 54 of FIG. 1.

From FIGS. 3-3B and 4-4B it should be apparent that the direction-changeoutput signal 222 and the direction-change output signal 272, both ofwhich correspond to the direction-change output signal 38 of FIG. 1 orthe direction-change output signal 32 of FIG. 1, can provide anindication of whether the ferrous gear is experiencing rotationalvibration or is rotating in normal operation. Therefore, rotationalvibration can be detected.

Referring now to FIG. 5, waveforms are shown that are associated withthe direction-agreement processor 40 of FIG. 1. Portions of magneticfield signals 302, 304 from zero to four on a time scale arerepresentative of magnetic fields that would be experienced by thesensor 10 of FIG. 1 if the sensor 10 were in proximity, for example, toa rotating ferrous gear experiencing rotational vibration. Otherportions of the magnetic field signals 302, 304 from four to six on thetime scale are representative of magnetic fields that would beexperienced by the sensor 10 in response to a continuous unidirectionalrotation of the ferrous gear in normal operation. It can be seen thatneither the portions of the waveforms 302, 304 between zero and four northe portions between four and six are necessarily pure sine waves.

Neither LDIFF and RDIFF signals nor thresholds corresponding to thethresholds th1-th4 of FIGS. 3A and 4A are shown. However, LDIFF andRDIFF signals (not shown) are generated and are compared to thresholdsas described in conjunction with FIGS. 3B and 4B, for example, inassociation with the left channel threshold detector 56 and the rightchannel threshold detector 22 of FIG. 1, to generate an LThreshOutsignal 306 and an RThreshOut signal 308 corresponding to the LThreshOutsignal 62 and the RThreshOut signal 26 of FIG. 1. As described above inconjunction with FIGS. 3-3B, the thresholds correspond to the thresholds135, 178 of FIG. 2, each of which can have two values.

Other thresholds are also applied to the LDIFF signal (not shown) and tothe RDIFF signal (not shown), for example, by the left channelpeak-referenced detector 54 and the right channel peak-referenceddetector 20 of FIG. 1 to generate an LPeakOut signal 310 and an RPeakOutsignal 312 corresponding to the LPeakOut signal 60 and the RPeakOutsignal 24 of FIG. 1. These other thresholds can correspond, for exampleto the thresholds 134, 176 of FIG. 2, each of which can have two values.

In operation, the LThreshOut signal 306 is compared with the RThreshOutsignal 308 by the direction-agreement processor 40 (FIG. 1) to providean output signal ThreshDirOut 314 indicative of which signal, LThreshOutor RThreshOut, has leading edges. As shown, during the time from zero tofour on the time scale, corresponding to a rotational vibration of theferrous gear, both the rising and falling edges of the LThreshOut signal306 lead the rising and falling edges of the RThreshOut signal 308. Thesame relationship applies during the time from four to six on the timescale, corresponding to normal unidirectional rotation of the ferrousgear. Having a continuous leading edge relationship, regardless ofwhether the ferrous gear is experiencing rotational vibration or arotation in normal operation, results in a ThreshDirOut signal 314 thatdoes not change state.

Furthermore, in operation, the LPeakOut signal 310 is compared with theRPeakOut signal 312 to provide an output signal PeakDirOut 316indicative of which signal, LPeakOut or RPeakOut, has leading edges. Asshown, during the time from zero to four on the time scale,corresponding to a rotational vibration of the ferrous gear, both therising and falling edges of the LPeakOut signal 310 lag the rising andfalling edges of the RPeakOut signal 312. The opposite relationshipapplies during the time from four to six on the time scale,corresponding to a normal rotation of the ferrous gear, where both therising and falling edges of the LPeakOut signal 310 lead the rising andfalling edges of the RPeakOut signal 312. Having opposite relationshipsat times when the ferrous gear is experiencing rotational vibration ascompared to times when the ferrous gear is experiencing rotation innormal operation results in a PeakDirOut signal 316, which changes stateat time four (e.g., PeakDirOut 316 is in a high state between the timeszero to four and in a low state between the times four to six).

It should be recognized that the state of the ThreshDirOut signal 314and the state of the PeakDirOut signal 316 are associated with adirection of rotation of the ferrous gear. Therefore, in the time periodfrom zero to four, the ThreshDirOut signal 314 and the PeakDirOut signal316 having different directions of rotation (i.e., they do not agree)and in the time period from four to six they indicate the same directionof rotation (i.e., they agree). Therefore, an agreement (i.e., theThreshDirOut signal 314 and the PeakDirOut 316 having the same state)provides an indication of a rotation in normal operation and adisagreement (i.e., the ThreshDirOut signal 314 and the PeakDirOut 316having different states) provides an indication of a rotationalvibration.

The ThreshDirOut signal 314 and the PeakDirOut signal 316 are combinedto provide a direction-agreement output signal 318 corresponding, forexample, to the direction-agreement output signal 42 of FIG. 1, whichprovides an indication of whether the ferrous gear is experiencingrotational vibration or is rotating in normal operation. Therefore, avibration can be detected.

Referring now to FIG. 6, waveforms 352, 354 are shown, which areassociated with the phase-overlap processor 46 of FIG. 1. The waveforms352, 354 are representative of magnetic fields that would be experiencedby the sensor 10 of FIG. 1 if the sensor 10 were in proximity, forexample, to a rotating ferrous gear continuously rotating in normaloperation. More particularly, the waveform 352 is representative of themagnetic field experienced by the magnetic field sensors 14 a, 14 b(FIG. 1) and the magnetic field signal 354 is representative of themagnetic field experienced by the magnetic field sensors 14 b, 14 c(FIG. 1) in response to a rotation in normal operation.

As described above in conjunction with FIG. 4, in normal operation,because of a separation between magnetic field sensors, the magneticfield experienced by the magnetic field sensors 14 a, 14 b (i.e.,waveform 352) is generally out of phase from the magnetic fieldexperienced by the magnetic field sensors 14 b, 14 c (i.e., waveform354). For example, in one particular embodiment described above inconjunction with FIG. 4, the waveforms 352, 354 are out of phase byabout forty degrees.

First signal regions 356 a, 356 b are selected to be a firstpredetermined percentage range of the peak-to-peak amplitude of thewaveform 352. Second signal regions 358 a, 358 b are similarly selectedto be the first predetermined percentage range of the peak-to-peakamplitude of the waveform 354. In one particular embodiment, the firstpredetermined percentage range is seventy percent to eighty-fivepercent.

Third signal regions 360 a, 360 b are selected to be a secondpredetermined percentage range of the peak-to-peak amplitude of thewaveform 352. Fourth signal regions 362 a, 362 b are similarly selectedto be the second predetermined percentage range of the peak-to-peakamplitude of the waveform 354. In one particular embodiment, the secondpredetermined percentage range is fifteen percent to thirty percent.

The first and second predetermined percentage ranges are selected sothat the first signal regions 356 a, 356 b do not overlap the secondsignal regions 358 a, 358 b and the third signal regions 360 a, 360 b donot overlap the fourth signal regions 362 a, 363 b, when the ferrousgear is rotating in normal operation.

Referring now to FIG. 7, waveforms 402, 404 are shown, which areassociated with the phase-overlap processor 46 of FIG. 1. The waveforms402, 404 are an RDIFF signal 402 and an LDIFF signal 404, which arerepresentative of magnetic fields that would be experienced by thesensor 10 of FIG. 1 if the sensor 10 were in proximity, for example, toa rotating ferrous gear experiencing translational vibration. Moreparticularly, the waveform 402 is representative of the magnetic fieldexperienced by the magnetic field sensors 14 a, 14 b (FIG. 1) and themagnetic field signal 404 is representative of the magnetic fieldexperienced by the magnetic field sensors 14 b, 14 c (FIG. 1) inresponse to the translational vibration.

As described above in conjunction with FIG. 6, when the ferrous gear isrotating in normal operation, magnetic fields experienced by themagnetic field sensors will be out of phase due to separation of themagnetic field sensors. However, as shown in FIG. 7, when experiencingtranslational or rotational vibration, even with the separation of themagnetic field sensors, the magnetic fields experienced are generally inphase (but can also be one hundred eighty degrees out of phase).Therefore, in the same way as the first, second, third and fourth signalregions 356 a-356 b, 358 a-358 b, 360 a-360 b, 362 a-362 b are describedin conjunction with FIG. 6, first and third signal regions 406 a-406 eand 408 a-408 d respectively can be associated with the waveform 402 andsecond and fourth signal regions 410 a-410 e and 412 a-412 drespectively can be associated with the waveform 404. Because thewaveforms 402, 404 are essentially in phase, the first signal regions406 a-406 e of the waveform 402 overlap the second signal regions 410a-410 e of the waveform 404 in time and the third signal regions 408a-408 d of the waveform 402 overlap the fourth signal regions 412 a-412d of the waveform 404 in time.

If the signals 402, 404 were one hundred eighty degrees out of phase asdescribed above, it is also possible that the first and fourth signalregions could overlap, for example, the first signal region 406 a andfourth signal region 412 a. Also the second and third signal regionscould overlap, for example, the second signal region 410 a and the thirdsignal region 408 a.

A high state of a phase flag signal 420 (phase_flag_l) indicates timesduring which the LDIFF signal 404 is within the regions 410 a-410 e and412 a-412 d, and a high state of a phase flag signal 422 (phase_flag_r)corresponds to times during which the RDIFF signal 402 is within theregions 406 a-406 e and 408 a-408 d. A left-right coincident signal 424(lr_coincident) corresponds to an overlap of the phase flag signals 420,422 being in a high state (i.e., an AND function is applied).

Therefore, the left-right coincident signal 420 provides an indicationof a translational or rotational vibration. The left-right coincidentsignal 420 can correspond, for example, to the phase-overlap outputsignal 48 of FIG. 1, which can provide an indication of whether theferrous gear is experiencing translational vibration or is rotating innormal operation. Therefore, a vibration can be detected.

Each of the direction-change output signal (e.g., 38 and/or 32, FIG. 1),the direction-agreement output signal (e.g., 42, FIG. 1), and thephase-overlap output signal (e.g., 48, FIG. 1) can provide informationregarding vibration of the ferrous object, and the output signals 32,38, 41, 48 can be used individually or in any combination of two, three,or four output signals to provide an indication of a vibration. To thisend, the combining processor 34 (FIG. 1), is responsive to two or moreof the vibration processor output signals 32, 38, 42, 48 for generatingthe vibration-decision output signal 80.

FIGS. 8-10 and 14-14A show flowcharts illustrating techniques, whichwould be implemented in an electronic device or in a computer processor.Rectangular elements (typified by element 452 in FIG. 8), herein denoted“processing blocks,” can represent computer software instructions orgroups of instructions. Diamond shaped elements, herein denoted“decision blocks,” can represent computer software instructions, orgroups of instructions that affect the execution of the computersoftware instructions represented by the processing blocks.

Alternatively, the processing and decision blocks represent stepsperformed by functionally equivalent circuits, such as a digital signalprocessor circuit or application specific integrated circuit (ASIC), ordiscrete electrical components. The flow diagrams do not depict thesyntax of any particular programming language. Rather, the flow diagramsillustrate the functional information one of ordinary skill in the artrequires to fabricate circuits or to generate computer software toperform the processing required of the particular apparatus. It will beappreciated by those of ordinary skill in the art that unless otherwiseindicated herein, the particular sequence of blocks described isillustrative only and can be varied without departing from the spirit ofthe invention. Thus, unless otherwise stated, the blocks described beloware unordered meaning that, when possible, the steps can be performed inany convenient or desirable order.

Referring now to FIG. 8, a process 450 of generating a direction-changeoutput signal (e.g., signal 38, FIG. 1) begins at block 452, where afirst rotation detector provides an output signal. In one illustrativeembodiment, the first rotation detector is the left channel thresholddetector 56 of FIG. 1 having the output signal 62 (LThreshOut) ofFIG. 1. At block 454, a second rotation detector provides an outputsignal. In one illustrative embodiment, the second rotation detector isthe right channel threshold detector 22 of FIG. 1 having the outputsignal 26 (RThreshOut) of FIG. 1.

At block 456, a change in direction of rotation is identified from theoutput signals provided by the first and second rotation detectors. Theidentification can be provided, for example, by the process 500described in conjunction with FIGS. 8A and 8B.

At block 458, a direction-change output signal is generated in responseto the change of direction identified at block 456. For example, thedirection-change output signal can be the direction-change output signal38 of FIG. 1. In one particular embodiment, the direction-change outputsignal can be a simple signal state. For example, the direction-changeoutput signal can be high when a direction change is identified at block456 and low when no direction change is identified at block 456. Inother embodiments, the direction-change output signal can be encoded toindicate a direction change or a lack of direction change.

Referring now to FIGS. 8A and 8B, an exemplary process 470 can be usedto identify a direction change associated with a rotation of the ferrousobject corresponding to block 456 of FIG. 8. At block 472, if a risingor a falling edge is detected in either the output signal from the firstrotation detector or in the output signal from the second rotationdetector, the process proceeds to step 474. If no edge is detected, theprocess loops at block 472. As noted above, in one illustrativeembodiment, the first rotation detector is the left channel thresholddetector 56 of FIG. 1 having the output signal 62 (LThreshOut), and thesecond rotation detector is the right channel threshold detector 22 ofFIG. 1 having the output signal 26 (RThreshOut).

If an edge is detected, at block 474 it is determined whether the edgedetected at block 472 was a rising edge in the output signal from thefirst rotation detector and the output signal from the second rotationdetector was low at the time of the rising edge from the first rotationdetector. If this condition is met, the process proceeds to block 484,where it is deemed that the rotation is in a first direction. If thiscondition is not met, then the process proceeds to block 476.

At block 476, it is determined whether the edge detected at block 472was a rising edge in the output signal from the second rotation detectorand the output signal from the first rotation detector was low at thetime of the rising edge from the second rotation detector. If thiscondition is met, the process proceeds to block 484, where it is deemedthat the rotation is in the first direction. If this condition is notmet, then the process proceeds to block 478.

At block 478, it is determined whether the edge detected at block 472was a falling edge in the output signal from the first rotation detectorand the output signal from the second rotation detector was high at thetime of the falling edge from the first rotation detector. If thiscondition is met, the process proceeds to block 484, where it is deemedthat the rotation is in the first direction. If this condition is notmet, then the process proceeds to block 480.

At block 480, it is determined whether the edge detected at block 472was a falling edge in the output signal from the second rotationdetector and the output signal from the first rotation detector was highat the time of the falling edge from the second rotation detector. Ifthis condition is met, the process proceeds to block 484, where it isdeemed that the rotation is in a first direction. If this condition isnot met, the process continues to block 482 where it is deemed that therotation is in a second direction.

From block 482, the process proceeds to decision block 486, where it isdetermined if the previously detected rotation was in the seconddirection. If the previously detected rotation was not in the seconddirection, then at block 488, the process 470 indicates a change indirection of rotation.

From block 484, the process proceeds to decision block 490, where it isdetermined if the previously detected rotation was in the firstdirection. If the previously detected rotation was not in the firstdirection, then at block 488, the process 470 indicates a change indirection of rotation.

If at decision block 486, the previously detected rotation was in thesecond direction, or if at decision block 490, the previously detectedrotation was in the first direction, then at block 492, the process 470indicated no change in direction of rotation.

It should be apparent that the conditions of blocks 474-480 correspondto edges 212, 214, 218, 220 described in conjunction with FIG. 3B.

Referring now to FIG. 9, a process 500 of generating adirection-agreement output signal (e.g., 42, signal FIG. 1) begins atblock 502, where a first direction of rotation is detected. In oneembodiment, the first direction of rotation is associated with the leftchannel threshold detector 56 and the right channel threshold detector22 of FIG. 1. Direction of rotation can be detected by the process shownin FIGS. 8A and 8B.

At block 504, a second direction of rotation is detected. In theillustrative embodiment, the second direction of rotation is associatedwith the left channel peak-referenced detector 54 and the right channelpeak-referenced detector 20 of FIG. 1. Again, direction of rotation canbe detected by a process such as the process shown in FIGS. 8A and 8B.

At block 506, it is determined if the first and second directions ofrotation identified at blocks 502 and 504 respectively agree with eachother. If the directions do not agree, at step 508, adirection-agreement output signal is generated that indicates avibration of the ferrous gear. If the directions do agree, at step 508 adirection-agreement output signal is generated that indicates rotationin normal operation. The direction-agreement output signal cancorrespond, for example, to the direction-agreement output signal 42 ofFIG. 1.

Referring now to FIG. 10, a process 550 of generating a phase-overlapoutput signal (e.g., signal 42, FIG. 1) begins at block 552, where amagnetic field is detected at a first location relative to the ferrousobject to provide an LDIFF signal. The first location can correspond,for example to a location of a center between the magnetic field sensors14 b, 14 c of FIG. 1, and the LDIFF signal corresponds to the LDIFFsignal 58 of FIG. 1 or the LDIFF signal 158 of FIG. 2.

At block 554, a magnetic field is detected at a second location toprovide an RDIFF signal. The second location can correspond, forexample, to a location of a center between the magnetic field sensors 14a, 14 b of FIG. 1, and the RDIFF signal corresponds to the RDIFF signal28 of FIG. 1 or the RDIFF signal 136 of FIG. 2.

At block 556, a first signal region is identified, which is associatedwith the RDIFF signal and a second signal region is identified, which isassociated with the LDIFF signal. The first signal region cancorrespond, for example, to the first signal regions 356 a, 356 b ofFIG. 6 and the second signal region can correspond, for example, to thesecond signal regions 358 a, 358 b of FIG. 6.

While first and second signal regions are described above in conjunctionwith block 556, it should be understood that in an alternatearrangement, third and fourth signal regions can also be used, forexample the third signal regions 360 a, 360 b and the fourth signalregions 362 a, 362 b of FIG. 6. The third and fourth signal regions canbe used in place of, or in addition to, the first and second signalregions.

At block 558, an overlap or lack of overlap of the first and secondsignal regions is identified. In the alternate arrangement describedabove, an overlap or lack of overlap of the third and fourth signalregions can also be identified. In still other arrangements, an overlapor lack of overlap of the first and fourth signal regions and/or thesecond and third signal regions is also identified.

At block 560, if an overlap of the first and second regions isidentified at block 558 (and/or an overlap of the third and fourthsignal regions), a phase-overlap output signal is generatedrepresentative of a vibration of the ferrous gear. If a lack of overlapof the first and second signal regions is identified at block 558(and/or a lack of overlap of the third and fourth signal regions) thenthe phase-overlap output signal is generated representative of arotation of the ferrous gear in normal operation. The phase-overlapoutput signal can correspond, for example, to the phase-overlap outputsignal 48 of FIG. 1.

Based upon the vibration detections indicated by the combining processor34 of FIG. 1, calibrations associated with the right channel offsetcontrol 106, the right channel offset DAC 108, a left channel offsetcontrol 144, a left channel offset DAC 146, and the shared AGC DAC 152,all shown in FIG. 2, can be avoided while a vibration is detected.

Referring now to FIG. 11, in which like elements of FIG. 1 are shownhaving like reference designations, an exemplary sensor 600 includes avibration processor 602. The vibration processor 602 is similar to thevibration processor 13 of FIG. 1, however, the vibration processor 602includes a running-mode processor 604 to provide arunning-mode-vibration output signal 606 to a combining processor 608.The combining processor 608 is similar to the combining processor 34 ofFIG. 1, however, the combining processor 608 has an additional input toreceive the running-mode-vibration output signal 606.

The running-mode processor 604 can be but one processor within thevibration processor 602 capable of detecting a vibration. For example,the running-mode-vibration output signal 606 can be combined withoutputs 32, 38, 42, 48 from others of the processors 30, 36, 40, 46described above in conjunction with FIG. 1, each capable of detecting avibration. The combining processor 608 can provide thevibration-decision output signal 80 indicative of whether or not theobject, e.g., the ferrous gear 11, is vibrating.

Referring now to FIGS. 12-12B, waveforms are shown which are associatedwith the running-mode processor 604 of FIG. 11 in response to avibration. Referring first to FIG. 12, waveforms 652 and 654, shown byphantom lines, represent magnetic fields experienced by the sensor 600of FIG. 11 if the sensor 600 were in proximity, for example, to therotating ferrous gear 11 (FIG. 11) continuously rotating in normaloperation. Portions 652 a, 654 a of the magnetic field signals 652, 654,however, are representative of magnetic fields that would be experiencedby the sensor 600 in response to a vibration of the ferrous gear 11.More particularly, the magnetic field signal 652 a is representative ofthe magnetic field experienced by the magnetic field sensors 14 a, 14 b(FIG. 11) and the magnetic field signal 654 a is representative of themagnetic field experienced by the magnetic field sensors 14 b, 14 c(FIG. 11) in response to the vibration.

A complete cycle of the magnetic fields 652, 654 corresponds to onetooth of the ferrous gear passing by the sensor 600, which generallycorresponds to only a small portion of a complete revolution of theferrous gear. The magnetic field signals 652 a and 654 a associated withthe vibration are bounded by a region between phases φ1 and φ2. Theregion between phases φ1 and φ2, therefore, corresponds to an evensmaller portion of a complete rotation of the ferrous gear 11.

While shown in one position on a time scale, the region between phasesφ1 and φ2 can be at any position on the time scale. Furthermore, it willbe appreciated that the phases φ1 and φ2 can have any separation. Alarger separation corresponds to a larger magnitude vibration and asmaller separation corresponds to a smaller magnitude vibration.

While the magnetic fields 652, 654 have a frequency associated with therotation of the ferrous gear in normal operation, it should beappreciated that the magnetic fields 652 a, 654 a can be experienced atany frequency by the sensor 600 (FIG. 11), determined by a rate ofvibration. For example, the ferrous gear 11 rotating back and forthabout its axis of rotation, or otherwise vibrating, causes the sensor600 to experience the magnetic fields 652 a, 654 a at the frequency ofthe vibration.

Referring now to FIG. 12A, the sensor 10 generates an LDIFF signal 656and an RDIFF signal 658. The LDIFF signal 656 can correspond, forexample, to the LDIFF signal 58 shown in FIG. 11, and the RDIFF signal658 can correspond, for example, to the RDIFF signal 28 of FIG. 11. Itwill be apparent from the magnetic fields 652 a, 654 a shown in FIG. 12,that the LDIFF signal 656 can have a greater magnitude than the RDIFFsignal 658. However if the region bounded by φ1 and φ2 (FIG. 12) were tobe at a different position along the time scale in FIG. 12, it isequally possible for the LDIFF signal 656 and the RDIFF signal 658 tohave other magnitude relationships. In response to a vibration, theLDIFF signal 656 and the RDIFF signal 658 are approximately in phase.

The LDIFF signal 656 and the RDIFF signal 658 can have different waveshapes depending, for example, on slopes in the region bounded by φ1 andφ2 of FIG. 12, and on the nature of the vibration. For example, theLDIFF signal 656 has a substantially triangular shape whereas the RDIFFsignal 658 has a substantially sinusoidal shape.

Furthermore, as described above, the region bounded by φ1 and φ2 (FIG.12) can be at any position and have any separation relative to themagnetic field signals 652, 654.

Furthermore, the vibration associated with the region bounded by φ1 andφ2 can have any type of movement. Therefore, it should be recognizedthat the LDIFF signal 656 and the RDIFF signal 658 can be more complexwaveforms than those shown.

In operation, the LDIFF signal 656 is compared to thresholds th1 and th2and the RDIFF signal 658 and is compared to thresholds th3 and th4. Thethresholds th1, th2 correspond to two states of the threshold 135 ofFIG. 2 and the thresholds th3, th4 correspond to two states of athreshold 178 of FIG. 2.

Referring now to FIG. 12B, comparison of the LDIFF signal 656 to thethresholds th1 and th2 shown in FIG. 12A results in an LThreshOut signal660 having edges 662 a-662 d. However, because the RDIFF signal 658 issmaller than thresholds th3 and th4, comparison of the RDIFF signal 658to the thresholds th3 and th4 of FIG. 12A results in an RThreshOutsignal 664, which is unresponsive, i.e., has no edges. The LThreshOutsignal 660 can correspond, for example, to the LThreshOut signal 62 ofFIG. 11, and the RThreshOut signal 664 can correspond to the RThreshOutsignal 26 of FIG. 11.

As described above, in an alternate embodiment, the signals of FIGS.12-12B can be associated with the peak-referenced detectors 20, 54 ofFIG. 11, in which case, the thresholds th1-th4 are selected inaccordance with the left channel peak-referenced detector 54 and theright channel peak-referenced detector 20 of FIG. 11, and the LThreshOutsignal 660 and the RThreshOut signal 664 are instead an LPeakOut signal(not shown) and an RPeakOut signal (not shown) corresponding to theLPeakOut signal 60, 162 and an RPeakOut signal 24 of FIG. 11.

The LThreshOut signal 660 has rising edges 662 a-662 d and theRThreshOut signal 664 is unresponsive, i.e., has no edges. In operation,the running-mode processor 604 (FIG. 11) detects the unresponsive natureof the RThreshOut signal 664. If the RThreshOut signal 664 remainsunresponsive for a predetermined number of edges of the LThreshOutsignal 660, a state change 668 a in a running-mode-vibration outputsignal 666 is generated, which is indicative of the vibration. Forexample, four rising edges 662 a-662 d can be counted, after which, ifthe RThreshOut signal 664 remains unresponsive, therunning-mode-vibration output signal 666 changes state. Generation ofthe running-mode-vibration output signal 666 is further described inconjunction with FIGS. 14 and 14A.

The running-mode-vibration output signal 666 can correspond, forexample, to the running-mode-vibration output signal 606 of FIG. 11. Itwill become more apparent from the discussion below in conjunction withFIGS. 14-14A that a running-mode-vibration output signal 666 thatchanges state is indicative of a vibration and a running-mode-vibrationoutput signal 666 that does not change state is indicative of novibration, i.e., of a unidirectional rotation in normal operation.Therefore, a vibration can be detected.

It should be recognized that the waveforms shown in FIG. 12-12 brepresent one example of possible waveforms associated with a vibration.However, other waveforms can be shown to occur in the presence of avibration for which the LDIFF signal 656 and the RDIFF signal 658 areoppositely related in shape and amplitude, which in turn results in theLThreshOut signal 660 and the RThreshOut signal 664 being essentiallyinterchanged. However, it is also possible that the LDIFF signal 656 andthe RDIFF signal 660 can have waveform shapes resulting in no detectionof a vibration. In this case, any one of the other vibration detectors30, 36, 40, and 46 (FIG. 11) can detect the vibration.

Referring now to FIG. 13, an exemplary circuit 70 can provide at least aportion of the running-mode processor 604 of FIG. 11. The circuit 70includes first and second counters 672 and 674, which receive theLThreshOut signal 671 and the RThreshOut signal 673, which cancorrespond, for example, to signals 62, 26 of FIG. 11. The first counter672 counts edges of the LThreshOut signal 671 and the second counter 674counts edges of the RThreshOut signal 673. The first counter 672 isreset with edges of the RThreshOut signal 673 and the second counter 674is reset with edges of the LThreshOut signal 671.

A first count decoder 676 detects if a digital count from the firstcounter 672 has exceeded a first count value, denoted as CNT_MAX1, and,in response thereto, generates a state change in a first intermediatesignal 676 a indicative of a vibration. Similarly, a second countdecoder 678 detects if a digital count from the second counter 674 hasexceeded a second count value, identified as CNT_MAX2, and, in responsethereto, generates a state change in a second intermediate signal 678 aindicative of the vibration. An OR gate 680 receives the first andsecond intermediate signals 676 a, 678 a. In response to either of theintermediate signals 676 a, 678 a indicating the vibration, therunning-mode-vibration output signal 682 indicates the vibration. Therunning-mode-vibration output signal 682 can correspond, for example, tothe running-mode-vibration output signal 606 of FIG. 11.

The first and second count values, CNT_MAX1 and CNT_MAX2 can be the sameor different. In one particular embodiment, both the first and secondcount values are four.

Referring now to FIG. 14, a process 700 associated with the running-modeprocessor 604 of FIG. 11 and with the circuit 70 of FIG. 13 begins atblock 702, where a first rotation detector provides an output signal,for example, the LThreshOut signal 62, 671 of FIGS. 11 and 13,respectively. Similarly, at block 704, a second rotation detectorprovides an output signal 26, 673, for example, the RThreshOut signal26, 673 of FIGS. 11 and 13, respectively.

At block 706, an unresponsive output from the first or second rotationdetectors is identified. For example, the unresponsive output cancorrespond to the unresponsive RThreshOut signal 664 of FIG. 12B. Atblock 706, a running-mode-vibration output signal is generated inresponse to the identified unresponsive output. Therunning-mode-vibration output signal can correspond, for example, to therunning-mode-vibration output signal 666 of FIG. 12B having the edge 668a.

Referring now to FIG. 14A, a process 750 can be used to identify anunresponsive output signal in accordance with block 706 of FIG. 1 and togenerate the running-mode-vibration output signal in accordance withblock 708 of FIG. 14. The process 750 also corresponds to functionsassociated with the circuit 70 of FIG. 13.

The process 750 begins at decision block 752, where the process 750loops waiting for an edge in the output signals from either a first or asecond rotation detector. For example, the edge can be either in theLThreshOut signal 62, 671 or in the RThreshOut signal 26, 673 of FIGS.11 and 13, respectively.

If an edge is detected, the process 750 continues to decision block 754where a decision is made as to whether the edge was in the output signalfrom the first rotation detector. If the edge was from the firstrotation detector, the process continues to block 756.

At block 756, a second edge count is reset to zero. For example, thesecond counter 674 of FIG. 13 is reset to zero by the LThreshOut signal671.

At block 757, a second intermediate signal is set to zero. For example,the second intermediate signal 678 a of FIG. 13 is set to zero.

At block 758 a first edge count is incremented by one. For example astate of the first counter 672 of FIG. 1 is incremented by one.

At decision block 760, it is decided whether the count of the firstcounter is less than or equal to (LE) a first predetermined count and ifthe count of the second counter is less than or equal to a secondpredetermined count. The first predetermined count can correspond, forexample, to the CNT_MAX1 of FIG. 13 and the second predetermined countcan correspond to the CNT_MAX2 of FIG. 13.

If both of the above described conditions are not met, then the processcontinues to decision block 764, where it is decided if the count of thefirst counter is greater than the first predetermined count. If thecount is greater, the process continues to block 766, where the firstintermediate signal is set to one. The first intermediate signal cancorrespond, for example, to the first intermediate signal 676 a of FIG.13.

At block 768, the running-mode-vibration output signal is set to one,corresponding to a detected vibration. The running-mode-vibration outputsignal can correspond, for example to the running-mode-vibration outputsignal 606 of FIG. 11, 666 of FIG. 12B, and 682 of FIG. 13. The processreturns to the decision block 752 and loops waiting for another detectededge.

If at decision block 760, it is determined that the condition is met,the process proceed to block 762, where the running-mode-vibrationoutput signal is set to zero. The process returns to the decision block752 and loops waiting for another detected edge.

If at decision block 754, the detected edge is not from the firstrotation detector, it must be from the second rotation detector, and theprocess continues at block 770, where the first edge count is set tozero. For example the first counter 672 of FIG. 13 is reset to zero.

At block 772 the first intermediate signal is set to zero. The firstintermediate signal can correspond, for example, to the firstintermediate signal 676 a of FIG. 13.

At block 774, the second edge count is incremented. For example thesecond counter 674 of FIG. 13 is incremented.

At decision block 776, it is decided whether the count of the firstcounter is less than or equal to (LE) the predetermined count and thecount of the second counter is less than or equal to the secondpredetermined count.

If both of the above described conditions are not met, then the processcontinues to decision block 780, where it is decided if the count of thesecond counter is greater than the second predetermined count. If thecount is greater, the process continues to block 782, where the secondintermediate signal is set to one. The second intermediate signal cancorrespond, for example, to the second intermediate signal 678 a of FIG.13.

At block 768, the running-mode-vibration output signal is set to one,corresponding to a detected vibration. The process returns to thedecision block 752 and loops waiting for another detected edge.

If at decision block 776, it is determined that the condition is met,the process proceed to block 762, where the running-mode-vibrationoutput signal is set to zero. The process returns to the decision block752 and loops waiting for another detected edge.

All references cited herein are hereby incorporated herein by referencein their entirety.

Having described preferred embodiments of the invention, it will nowbecome apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may be used. It is felttherefore that these embodiments should not be limited to disclosedembodiments, but rather should be limited only by the spirit and scopeof the appended claims.

1. Apparatus for detecting a vibration of an object adapted forrotation, comprising: a plurality of magnetic field sensors forgenerating an RDIFF signal proportional to a magnetic field at a firstlocation relative to the object and an LDIFF signal proportional to amagnetic field at a second location relative to the object; at least tworotation detectors, wherein a first one of the rotation detectors iscoupled to at least one of the magnetic field sensors and is responsiveto the RDIFF signal for providing a first output signal indicative ofrotation of the object and wherein a second one of the rotationdetectors is coupled to at least one of the magnetic field sensors andis responsive to the LDIFF signal for providing a second output signalindicative of rotation of the object; and a vibration processorresponsive to the first and second output signals from the at least tworotation detectors for detecting the vibration of the object, thevibration processor comprising one or more vibration detectorsincluding: a phase-overlap processor to identify a first signal regionassociated with the RDIFF signal and a second signal region associatedwith the LDIFF signal, to identify a first overlap as an overlap of thefirst signal region and the second signal region, and to generate aphase-overlap output signal indicative of the vibration of the object inresponse to the first overlap.
 2. The apparatus of claim 1, wherein theapparatus comprises two rotation detectors, each of a type selected froma peak-referenced detector and a threshold detector.
 3. The apparatus ofclaim 1, wherein the apparatus comprises four rotation detectors, eachof a type selected from a peak-referenced detector and a thresholddetector.
 4. The apparatus of claim 1, wherein the first signal regionis associated with a percentage range of a peak-to-peak magnitude of theRDIFF signal and the second signal region is associated with apercentage range of a peak-to-peak magnitude of the LDIFF signal.
 5. Theapparatus of claim 4, wherein the percentage range of the peak-to-peakmagnitude of the RDIFF signal is substantially equal to the percentagerange of the peak-to-peak magnitude of the LDIFF signal.
 6. Theapparatus of claim 1, wherein the one or more vibration detectorsincludes another different type of vibration detector, the vibrationprocessor further comprising a combining processor coupled to the one ormore vibration detectors to combine output signals of the one or morevibration detectors to generate a vibration-decision output signalindicative of the vibration of the object.
 7. The apparatus of claim 1,wherein the apparatus is configured for use in an automobile.
 8. Theapparatus of claim 1, wherein the first signal region is associated witha first percentage range spanning about seventy to eighty-five percentof a peak-to-peak magnitude of the RDIFF signal and the second signalregion is associated with the first percentage range spanning aboutseventy to eighty-five percent of a peak-to-peak magnitude of the LDIFFsignal.
 9. The apparatus of claim 1, wherein the phase-overlap processoris also to identify a third signal region associated with the RDIFFsignal and a fourth signal region associated with the LDIFF signal, toidentify a second overlap as an overlap of the third signal region andthe fourth signal region, and to generate the phase-overlap outputsignal indicative of the vibration of the object in response to thefirst and second overlaps.
 10. The apparatus of claim 9, wherein thefirst signal region is associated with a first percentage range spanningabout seventy to eighty-five percent of a peak-to-peak magnitude of theRDIFF signal, the second signal region is associated with the firstpercentage range spanning about seventy to eighty-five percent of apeak-to-peak magnitude of the LDIFF signal, the third signal region isassociated with a second percentage range spanning about fifteen toabout thirty percent of a peak-to-peak magnitude of the RDIFF signal,and the second signal region is associated with the second percentagerange spanning about fifteen to about thirty percent of a peak-to-peakmagnitude of the LDIFF signal.
 11. The apparatus of claim 1, furthercomprising an output protocol processor coupled to the vibrationprocessor, the output protocol processor for providing an output signalindicative of the vibration of the object and also indicative of therotation of the object.
 12. The apparatus of claim 11, wherein theoutput signal provided by the output protocol processor is indicative ofthe rotation of the object when no vibration is detected by thevibration processor, and wherein the output signal provided by theoutput protocol processor achieves a substantially static signal valuewhen a vibration is detected by the by the vibration processor.